2 Valadão et al. Initial development and biomass partitioning of Physocalymma scaberrimum Pohl (Lythraceae) under different shading levels Moreover, the agricultural frontier in Brazil has already advanced beyond the Cerrado border, penetrating into the Amazon forest and creating a wide region known as Arc of Deforestation (NOGUEIRA et al., 2008; NOGUEI- RA et al., 2007). Owing to this scenario and the increasing concern with respect to environmental quality, there is a strong increase in demand for forest services and products, especially forest species seedling production destined for several purposes (ALVES et al., 2012). This demand pressure arouses the necessity for researches in order to optimize the lowcost production of seedlings with morphophysiological qualities capable of fulfilling the final objectives of the plantation (JOSÉ et al., 2005). Therefore, it is necessary to conduct studies about native forest species in the Cerrado Biome and in the southern border of the Amazon. The development of suitable techniques for seedling production (SOUCHIE et al., 2011), for instance, is a crucial stage in the restoration of degraded areas and for commercial plantations, or even for the implementation of systems of Agriculture-Livestock-Forest integration aiming at recovering the production capacity of the land. Several studies have evaluated the early development of seedlings of different species in nursery, under the effect of controlled brightness, which gave different answers to the shading levels (MAZUCHOWSKI et al., 2007; NAKAZONO et al., 2001; 2007; SILVA et al., 2007). In most studies, the seedlings presented better response to intermediary brightness levels, with some variations in plant growth and vigor, and the best conditions were found between 30% and 70% shading. The light, as a primary source of energy related to photosynthesis, is one of the main factors affecting plant growth (CAMPOS; UCHIDA, 2002; DOUSSEAU et al., 2007), considering that distinct brightness levels cause morphologic and physiologic changes in the plant, with the adaptation driven by particular characteristics of each species in interaction with the environment (SCALON et al., 2003). Brightness influence on seedlings can be determined through the index of seedling quality (NAKAZONO et al., 2001., DUTRA et al., 2012;). This indicator uses parameters such as height, stem diameter and biomass, analyzed alone or together, which can be revealing if applied in seedlings developed under similar environmental conditions (FONSECA et al., 2002), as observed in studies by Azevedo et al. (2010), Chaves and Paiva (2004) and José et al. (2005). The formation of more vigorous seedlings provides a greater chance for success in the crop establishment and maximizes its growth while decreasing the transplantation time into the field (LIMA et al., 2008). The seedlings still must present greater shoot size and well-formed roots, so that they present higher surviving chances in the field (FERRAZ, 2011), especially under the seasonal conditions of the Cerrado Biome (MA- RIMON-JUNIOR et al. unpublished data). Exotic species such as Eucalyptus spp. and Tectona grandis have guaranteed their own success in reforestations owing to many years of research and improvement of large scale production techniques of their propagules (FER- MINO-JUNIOR et al., 2009; MACEDO et al., 2005; GOMES et al., 2002; GOMES et al., 1978; SANTOS et al., 2010). Nevertheless, the studies which take into account the plant growth performance in nursery and the silvicultural characteristics of native species are still scarce and not conclusive, despite some evidences of better root and shoot biomass production of seedlings at 50% shading (FELFILI et al., 1999). The continuous evaluation and followup of the processes of seedling production are important in order for us to learn about the physiologic responses of native species and to understand their ecology. Each response verified in these nursery experiments may also be used for the improvement of seedling production techniques, especially when quality criteria are taken into account. The neotropical woody species Physocalymma scaberrimum Pohl must be included in studies regarding the development of native forest seedlings in nursery due to its major potential for timber production and for restoration of degraded areas, or still for Agriculture-Livestock- Forest integration (MARIMON-JUNIOR et al.,unpublished data). According to the Lista de Espécies da Flora do Brasil 2013 (in this species is found in the North and Midwest of Brazil, as well as in the States of Acre, Pará, Goiás and Mato Grosso. This work aimed at evaluating the early development of Physocalymma scaberrimum Pohl seedlings in order to understand how its seedlings grow under distinct shading levels, as there is a lack of nursery studies with most of native tree species in the Cerrado and Amazon. The ex- 130

3 periment is part of the Matas de Galeria Project (FAPEMAT 0738/2006), whose objective is to enhance knowledge with regard to the ecology and expertise of the main native woody species in the Cerrado Biome and pre-amazonian transition forests. The main goal is to contribute to future ex-situ conservation actions for this species, as well as to sustainable activities and those regarding restoration of degraded areas or timber production and forest management. MATERIAL AND METHODS The experiment was carried out between December 2008 and April 2009, in the forest nursery of the State University of Mato Grosso (UNEMAT), Nova Xavantina campus, Mato Grosso State. The climate in the region is Aw, according to Köppen s classification, with two well-defined seasons: one dry, from April to September, and another rainy, from October to March (SILVA et al., 2008), with annual average rainfall ranging from 1,300 to 1,500 mm (MARIMON et al., 2010). Healthy seeds without signs of predation were collected in a preserved gallery forest in the Bacaba Municipal Park, municipality of Nova Xavantina-MT. The seeds were sown in black 15 x 30 cm polyethylene bags with lateral holes for water drainage. The substrate utilized was a mixture of weathered wood sawing and Red Oxisol in a 2:1 ratio, respectively. The fertilization was done with 350 g m -3 of NPK granular fertilizer and ph adjustment with 980 g m -3 of lime to improve the substrate (Table 1) and provide the basic nutritional requirements for P. scaberrimum, a tree species that occurs in soils with medium fertility in the Cerrado Biome. The substrate was mixed in an electric mixer for perfect homogenization. An extra dose of 0.5 g triple superphosphate was added in each bag so as to compensate the P fraction of the substrate inhibited by the alkaline action of the limestone. The seeds of P. scaberrimum were submitted to the following shading treatments described by Marimon et al. (2008): 0% (full sun), 30%, 50%, 70% and 90%, covered by a nylon shadescreen. Fifty plants were assessed in each shading level. The shading levels were established by measurements of the photosynthetic active radiation (PAR) in each treatment, by three measurements in the morning and three in the afternoon, using a LI-190 S quanta sensor (LI- COR Inc., USA). We used a no shaded control point to determine the measure of full sun. The levels of 30, 50 and 70% were obtained by using commercial screen Sombrite and 90% overlapping of two screens with 30% and 20% shading, all shading levels were confirmed by the inverse of PAR proportional comparison with the control (full sun). Daily irrigations were applied by micro spray, with daily application rate adjusted according to the microclimatic conditions assessed by the meteorological station of UNEMAT Nova Xavantina (OMM: 83319), latitude -14,7º, longitude -52,35º, altitude 316m. For each treatment we registered the number of germinated seeds within a period of 22 days and later evaluated the percentage and Germination Velocity Index (GVI), we considered germinated seeds that showed full stretch hypocotyl over the substrate. The germination velocity calculation was performed according to Maguire (1962), where: GVI = S (Gi/ni); Gi = number of germinated seeds and ni = counting day. Seedling height was measured from the base to the apical bud by a clear millimeter rule, with point zero placed at the base of the plant. Stem diameter was measured by a digital caliper (0.02 mm precision) positioned at the base of the stem. The number of leaves was manually counted, considering only the fully-expanded leaves. These parameters were first assessed 150 days after seedling emergence (DAE) and, afterwards, at 180, 210, 240 and 270 DAE. At the end of the experiment (270 DAE), ten seedlings of each treatment were used to assess root and shoot dry biomass. The roots were separated from the substrate by a water wash. Root and shoot parts were separated, identified, dried in oven at 80 C until constant weight, and then weighed on a precision scale. Table 1. Chemical characteristics of the substrate used to produce Physocalymma scaberrimum seedlings in forest nursery. Tabela 1. Atributos químicos do substrato utilizado na produção de mudas de Physocalymma scaberrimum em viveiro florestal. P K Ca Mg Al SB C.E.C. O.M. (V) Ca/Mg ph (H 2 O) mg dm -3 cmol c dm -3 (%) 6,7 24, ,6 0,53 0,0 2,9 3,6 10,2 80,5 3,01 SB = sum of bases; CEC = cation exchange capacity; O.M. = organic matter; V = base saturation 131

4 Valadão et al. Initial development and biomass partitioning of Physocalymma scaberrimum Pohl (Lythraceae) under different shading levels In order to determine the differences regarding quality/size in the seedlings development, the quality standard was evaluated through Dickson quality index (DQI) (DICKSON et al., 1960), through the formula: DQI = TDM/ ((H/D)+(SDM/RDM)), where TDM = Total dry mass (g); H = shoot height (cm); D = stem diameter (mm); SDM = Shoot dry mass (g); and RDM = root dry mass. This index weighs the root/shoot ratio and the allometric relations between height and diameter, once the etiolated seedlings or those with lower root development must be considered as low-quality due to their stress sensibility in field conditions. We also calculated the relationship between height and shoot dry mass (H/SDM). The differences in seedlings development parameters among treatments were tested by analysis of variance (One-Way ANOVA) followed by Tukey s test, whenever there was difference between averages at the 5% significance level. Data normality was verified by Shapiro-Wilk s test and homogeneity of variances by Levene s test. For samples whose Levene s value was lower than 0.05, data were transformed by Log10. If the presuppositions were not fulfilled, the Kruskal- Wallis test was carried out (SIEGEL; CASTEL- LAN-JÚNIOR, 1988), followed by Dunnett test at 5% probability. In order to verify the relation between brightness and diameter, height and number of leaves a regression analysis was done; the model which best fitted the dataset was used. The analyses were carried out through the software BioEstat 5.0 (AYRES et al., 2007). RESULTS Germination The results for Germination Velocity Index (GVI) and the percentage of germination of Physocalymma scaberrimum seeds are presented in Table 2. The P. scaberrimum seeds were sown immediately after harvest and began the germination process on the third day, up to 18 days after sowing in all treatments. The GVI and the percentage of germinated seeds were high in all treatments but not influenced by shading levels. Table 2. Effect of different shading levels in Germination Speed Index (GVI) and total germination (%) for Physocalymma scaberrimum seeds in forest nursey. Tabela 2. Efeito dos diferentes níveis de sombreamento no Índice de Velocidade de Germinação (IVG) e germinação total (%) para sementes de Physocalymma scaberrimum em viveiro florestal. Treatment GVI (%) Germination 0% 0.299a 100a 30% 0.426a 100a 50% 0.340a 100a 70% 0.330a 100a 90% 0.284a 92a Means followed by the same letter do not differ significantly by Tukey and Dunnet tests at 5% probability. Height Shading levels influence on P. scaberrimum seedlings height (cm) followed a similar pattern. The 30%, 50% and 70% shading levels presented the highest mean height values and did not differ from each other in any of the five sampling periods (Table 3). The seedlings submitted to extreme brightness (full sun) and shading (90%) levels showed average heights significantly lower than the other treatments, but did not statistically differ from each other (Table 3). Diameter Stem diameter also showed a similar pattern of performance under intermediary shading levels (30, 50 and 70%), not significantly differing from each other in any of the evaluations (Table 3). Only the full-sun treatment did not differ from the 30% shading treatment in the evaluation at 180 DAE and from that of 70% shade at 240 DAE. The seedlings in the highest shading (90%) treatment presented average stem diameter values significantly lower than all other treatments at 180, 210 and 240 DAE (Table 3). We found significant differences at 210, 240 and 270 DAE for the 50% shading in the regression tests for stem diameter in relation to the shading levels (Figure 1). The better performance of the seedlings under 50% shading can be observed, from the middle to the end of the experiment. Number of leaves The number of leaves in the P. scaberrimum seedlings followed a pattern of better response to the intermediary shading levels throughout time, presenting significant higher number of leaves in the 50% treatment compared to the others in the evaluation at 180 DAE (Table 3). 132

8 Valadão et al. Initial development and biomass partitioning of Physocalymma scaberrimum Pohl (Lythraceae) under different shading levels Diameter The intermediate levels of shade also favored the gain in diameter of P. scaberrimum seedlings. According to Larcher (2000), if there is no drastic change on the ground conditions, is kept linear logarithmic correlation between the mass of the stem and root mass (allometric growth). The significance pattern of the regression curves at 210, 240 and 270 days after seedling emergence, demonstrates the importance of this parameter. According to Gomes and Paiva (2004), the stem diameter is strongly correlated with other characteristics of seedlings, explaining 70-80% of differences in dry weight matter between them. In a study conducted by Rego and Possamai (2006), with Cariniana legallis (Mart.) Kuntze seedlings in the city of Colombo in Paraná state, they reduced the percentage of photosynthetically active radiation; which affected diameter growth resulting in a less developed the root system. The reduction of diameter in seedlings may affect their growth performance, condition clearly observed by reducing the Dickson quality index observed in studies with other forest species under controlled shading experiments (Marimon-Junior et al., unpublished data). Number of leaves The low tolerance at highest shading levels was also pointed out by Câmara and Endres (2008) in Maceió, state of Alagoas with Mimosa caesalpiniifolia Benth seedlings submitted to 92% shading, and with highest number of leaves in seedlings exposed to 50% shading. The species Simarouba amara assessed by Azevedo et al. (2010) in Manaus state of Amazonas presented similar performance. This response is similar to Hymenaea courbaril, a shade-tolerant tree species tested in nursery by Marimon-Junior et al. (unpublished data). Since the intermediate amount of light is responsible for the level of chlorophyll in the leaves, this condition tends to increase levels of the pigment in a and b forms (MARTINAZZO et al., 2007). However, the content of chlorophyll b is better correlated to shaded environments (ENGEL; POGGIANI, 1991), since it allows the capture of energy in other wavelengths than chlorophyll a, in order to maintain the nutritional equilibrium of the plant (WHATLEY; WHATLEY, 1982). We did not evaluate this condition, but new studies must be conducted to investigate whether the higher levels of shade are compensated or not by an increase in b chlorophyll concentrations in the leaves. Biomass The root/shoot relation (RSR) is an important quality criteria for seedlings, since those with a more developed shoot portion than the root (RSR<1) can be more sensitive to water stress under conditions of high air temperature and low relative humidity during dry seasons (LARCHER, 2000), as found in the Cerrado Biome (SILVA et al., 2008). Similar results were observed in young seedlings of Brosimum rubescens Taub. from seeds collected in a transitional Amazonia/Cerrado monodominant forest in study conducted by Marimon et al.(2008). The authors emphasize that higher investment in root biomass under low-shading conditions is evidence that root development is necessary for seedling survival in natural conditions of high brightness (large gaps) and seasonal water deficit. Although the parameter of total biomass has shown a significant correlation with the levels of shading, we used the biomass partitioned tests in order to analyze each part of the plant separately. This is because when a pattern of quality is not based on partitioned plant, but only on the total weight, it weakens the recommendations. Dickson quality index (DQI) Based on the fact that the lowest values of allometric relations are those in which the divisor is height (H/SDM and SDM/RDM), we affirm that P. scaberrimum tends to invest more in crown-related volume than in total height under intermediary brightness conditions. This response may possibly be due to the fact that these conditions are similar to those found in the natural environment of this species, thus more suitable for this growth pattern. In this case, seedling quality tends to be better since investment in root follows the highest vegetative effort of the plant in the canopy total volumetric formation (DICKSON et al., 1960). Similar results were found in studies with seedlings of Senna macranthera (Collad.) Irwin et Barn conducted in Viçosa, state of Minas Gerais by Chaves and Paiva (2004). The authors verified decreases in the H/SDM relation when shading periods were increased. The lowest values that we found for such relationships were preponderant for the higher DQI presented by seedlings of P. scaberrimum at 50% shading. Although it did 136

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